PHOENIX (AP) — A scandal in which 6,000 child-abuse complaints in Arizona were filed away and never investigated illustrated what advocates say is a tragically common problem across the U.S.: Many child-protection agencies have crushing workloads and inadequate oversight.

In some cases, those flaws have led to deaths and criminal charges against social workers.

"This is a system that years ago was dubbed a poor system for poor people, and very often the resources are not there to do this very difficult and very important work," said Dr. Howard Dubowitz, a pediatrician who studies child protection policies at the University of Maryland Medical Center.

"The notion that this is a system that is nicely equipped to fulfill its mandate is often a dream that some of us are hanging onto."

Arizona officials promised prompt action after it was disclosed Thursday that over the past four years, a team at the state Child Protective Services agency tried to cope with the heavy workload by overlooking thousands of complaints to the statewide child-abuse hotline.

Under state law, all reports generated via the hotline must be investigated.

So far, authorities re-examining the cases have identified at least 125 in which children were later alleged to have been abused. No deaths have been connected to the lapses.

Clarence Carter, who as director of Arizona's Department of Economic Security oversees CPS, called the situation "cause for grave alarm," and Gov. Jan Brewer has ordered an investigation.

Child-welfare advocates said the Arizona debacle is not an isolated incident.

In North Carolina, a county social worker faces nearly four years in prison after pleading guilty to trying to cover up her agency's role after a child's death.

Prosecutors said that after the 2011 death of 15-month-old Aubrey Kina-Marie Littlejohn, social worker Candice Lassiter ordered a subordinate to falsify records to make it appear that the Swain County Department of Social Services had done a thorough job investigating allegations that the girl had been abused.

An Associated Press investigation found that police and social workers were aware of reports that the child was being mistreated but failed to act in time.

Florida's Department of Children and Families has long been plagued by problems blamed on heavy caseloads, high staff turnover, lack of accountability and inadequate funding.

Last year, the agency overhauled its own abuse hotline, which receives more than 400,000 calls a year, after problems were discovered with how information was collected and passed on to investigators, often without information about multiple calls on the same cases.

Lawmakers there are still grappling with how to fix the agency in light of the recent deaths of nine children monitored by DCF.

In May, the Florida agency fired an investigator who authorities say forged documents about substance treatment for a mother months before her baby was left to die in a sweltering car.

The agency's chief abruptly resigned in July.

The Michigan Human Services Department came under federal oversight in 2008 after it was accused of failing to protect children from abuse and neglect.

A report last month by federal monitors found some improvements but noted more still needed to be done.

In Arizona, CPS has long suffered from what defenders say is understaffing and overwork.

The number of abuse and neglect reports requiring investigation has risen 16 percent in the five years ending in March, according to the agency, while the number of children in foster care or other out-of-home oversight has surged from about 9,000 to nearly 15,000.

Meanwhile, the number of CPS workers has remained essentially flat, with the agency struggling with 20 percent annual turnover.

The 1,000 caseworkers assigned to child-welfare investigations have caseloads 77 percent above the standard, according to CPS. Carter is asking for an additional 350 workers in the coming budget.

The debacle has led to a new round of criticism of CPS and demands for Carter's resignation from some Democrats, but the governor, a fellow Republican, is standing by him.